We have investigated light propagation through a single line-defect photonic crystal waveguide on a InP membrane. Modal analysis was performed using the finite-difference time-domain method. The fundamental mode has been found to be very close to the fundamental mode in a “refractive” waveguide but, in this case, it is inherently leaky. The propagation losses of this mode in the complete three-dimensional structure have been computed and measured to determine if its use could be of interest for practical applications. Propagation losses in the range of 0.1 dB/μm have been found numerically and experimentally for the fundamental mode whereas stronger out-of-plane losses have been observed for the other leaky mode within the band gap. The origins of the out-of-plane losses were then investigated and have clarified the inherent lower leakage of the fundamental mode.

We report a systematic study of a grating formation in which the in sodium–magnesium–aluminosilicate glasses is varied from 0.76 to 8.11 mol %. The growth, decay, and erasure of the grating are reported as functions of the The maximum persistent change in the index of refraction was The persistent change in the index of refraction was initially a quadratic function of the and showed a limiting behavior at the highest The transient change in the index of refraction was a quadratic function of throughout the range of concentrations studied here. The grating buildup rate increased linearly with The results of this study are consistent with the model published recently by Dixon et al. Ionic conductivities were also measured to help separate the effect of the on the glass network from its active role in transferring the optical energy into ionic motion.

Semiconductor lasers with third-order waveguide mode emission are a promising route toward compact twin-photon sources. In these structures, emission on the third-order mode is required for satisfaction of the phase-matching condition between the pumping frequency and fundamental modes at half frequency and so the production of twin photons. Phase matching depends critically on sample temperature through the dependence of the effective refractive indices of the sample. The dependence of laser mode emission on the temperature of a semiconductor structure specially designed for third-order mode emission at 775 nm is studied. It is shown that the third-order mode emission is preserved up to 40 °C whereas a contribution from other modes becomes significant above that temperature.

The fabrication and characterization of an InGaN/GaN multiple-quantum well(MQW)light-emitting diode(LED) with a current blocking layer inserted beneath the p-pad electrode is described. The light-output power and external quantum efficiency for the InGaN/GaN MQWLED chip with a current blocking layer were significantly increased compared to those for the conventional InGaN/GaN MQWLED chip. The increase in the light-output power can be attributed to the injection of additional current into the light-emitting quantum well layer of the LED by the current blocking layer and a reduction in parasitic optical absorption in the p-pad electrode.

We investigate thermally induced transmission variations in a 3.6-μm-thick photonic band gapstructure by means of a pump–probe setup, in the 600–700 nm range, under cw pump conditions. An induced temperature increase is responsible for the thermal expansion of the layers, as well as changes in the index of refraction. As a result, the band gapstructure is redshifted by several nanometers. The initial transmission of the probe beam was restored following the removal of the pump laser, thus indicating the reversible nature of the process.

The transmission spectra of a three-dimensional photonic crystal for various incident angles was examined. When the incident angle is not normal to the surface of the crystal, the direction of the wave vector of light is sensitive to the frequency. In order to compare the experimental band edge with the theoretical band diagram, we calculated the band diagram of the frequency versus the incident angle by converting the ordinary band diagram, which is ordinarily expressed as the diagram of the frequency versus the internal wave vector. As a result of the comparison, the changes of the band edge which was obtained in the experimental transmission measurement agreed well with the theoretical changes. It became clear that the two-step attenuation of transmission which is at large incident angles is caused by the split of the first and the second band edge (also the third and the fourth band edge) at large incident angles.

Photostimulated nonlinear optical effects in synthesized (PGBC) glassesdoped by and rare-earth ions were discovered. Temperature-dependentmeasurements of optical photoinduced second-harmonic generation (PISHG) and two-photon absorption were performed in the infrared (IR) range. CO pulse laser (λ=5.5 μm, energy power density up to 3.8 per pulse) was applied as a source of IR-photoinducing and probing (fundamental) light. Absolute values of the PISHG were more than 22% higher than corresponding values obtained for other glasses: [1] or [2] type. The investigated PGBC system possesses a shorter time response (about 18 ps), compared with other IR nonlinear optical glasses. We have also established that all nonlinear optical susceptibilities are dependent on the type of ion. A maximal value of the PISHG is achieved for the glassesdoped by The PISHG values increase significantly below 25 K. We have carried out ab initio molecular dynamics and quantum chemical simulations in order to evaluate the possible contribution of electron–phonon anharmonic interactions in the observed phenomena. We have modeled the influence of the external CO photoinduced beam through the photoinduced anharmonic electron-phonon interactions. A decrease of the delaying time response is achieved. To obtain independent confirmation of the observed dependencies, we have carried out measurements of the during the external IR pumping. We have also compared the measured and theoretically calculated dependencies of the IR-induced effects.

The microwave induced plasmas have been successfully used as an excitation source in atomic emission and mass spectrometry for the analytical determination of substances. In this work a study of the influence of the thermodynamic equilibrium state over the capacity of sample excitation of an argon plasmaflame sustained by a surface wave at atmospheric pressure is presented. The state of the thermodynamic equilibrium in the discharge is determined by the relation between its temperatures and densities. The values of these parameters depend on the energy available in the discharge, which is also responsible for the excitation of the samples introduced into the plasma. We have compared the behavior of two characteristic parameters of plasma (electron density and temperature) and of the ArI level population with the microwave power. The results have shown that the values of these parameters and populations had a tendency to remain constant for microwave powers above a certain value. Thus, from 100 W only a part of the energy injected into the discharge is absorbed in the plasma and the plasma equilibrium state is not consequently modified. This behavior is the same as that found for atomic lines of both halogens and iron introduced as samples into the plasma and seems to show that if the plasma is close to thermodynamic equilibrium the excitation of the samples is favored.

The methane decomposition and the formation of hydrocarbons, in particular acetylene, in a microwave plasma were studied. It was found that pulsing the discharge presents major advantages over the cw operation. The effect of the operating parameters, including pressure (15–65 mbar), flow rate (33–190 sccm), and discharge power (16–81 W) was investigated, with the aim to improve the efficiency for methane conversion and to reduce the energy requirement for the formation of acetylene. Maximum values of the methane conversion degree over 90% were obtained. As a function of the discharge conditions, acetylene can become the main reaction product, with 80% selectivity. The minimum energy requirement for methane conversion was approximately 7 eV/molecule and for acetylene formation 20 eV/molecule. The results show that active species generated in the plasma contribute to the methanedissociation and influence the product distribution. The correlation between the dehydrogenation and the gas temperature supports the view of thermally activated neutral–neutral reactions.

The time-dependent current wave forms measured using a pulse biased planar electrode in hydrogen radio-frequency (rf), inductively coupled plasma,plasma immersion ion implantation experiments are observed to vary in the presence of an external magnetic field Results further indicate that the magnitude of the pulse current is related to the strength and direction of the magnetic field, rf power, and pressure, but the pulse current curves can be primarily correlated with The plasma discharges are enhanced in all cases due to magnetic confinement of the electrons, enlargement of the plasma generation volume, and increase in the rf power absorbing efficiency. The plasma density diagnosed by Langmuir probe diminishes in front of the sample chuck with whereas the plasma is confined nearby the sidewall of the vacuum chamber at high magnetic field. The high degree of plasma density nonuniformity at high in front of the sample chuck is not desirable for the processing of planar samples such as silicon wafers and must be compensated. The reduction in the plasma density and plasma density gradient in the sheath can be accounted for by the changes in the pulse current wave forms.

A comparison is made between a one-dimensional (1D) and a two-dimensional (2D) self-consistent fluid model for a methane rf plasma, used for the deposition of diamond-like carbon layers. Both fluid models consider the same species (i.e., 20 in total; neutrals, radicals, ions, and electrons) and the same electron–neutral, ion–neutral, and neutral–neutral reactions. The reaction rate coefficients of the different electron–neutral reactions depend strongly on the average electron energy, and are obtained from the simplified Boltzmann equation. All simulations are limited to the alpha regime, hence secondary electrons are not taken into account. Whereas the 1D fluid model considers only the distance between the electrodes (axial direction), the 2D fluid model takes into account the axial as well as the radial directions (i.e., distance between the electrodes and the radius of the plasma reactor, respectively). The calculation results (species densities and species fluxes towards the electrodes) obtained with the 1D and 2D fluid model are in relatively good agreement. However, the 2D fluid model can give additional information on the fluxes towards the electrodes, as a function of electrode radius. It is found that the fluxes of the plasma species towards both electrodes show a nonuniform profile, as a function of electrode radius. This will have an effect on the uniformity of the deposited layer.

We propose a method for determining the spatial distribution of population densities for the species in laser-produced plasma. Our method relies on the parameter fittings of the experimentally observed self-reversed emission profiles to the model which is based on the calculation of one-dimensional radiative transfer. Employed parameters in the model represent spatial distribution of emitters, absorbers, and plasma free electrons. Since the density of plasmaelectrons has a spatial dependence, Stark shifts and broadenings are incorporated in a position-sensitive manner. After a general description of the method, we have specifically applied it to the laser-ablated Al plasma, where Al(I) emission line is employed for the analysis. In this specific example, we find that the accuracy of the fittings is significantly improved due to the presence of two emission lines originating from the fine structure, i. e., and In particular, the depth of the self-reversed structure turns out to be very sensitive to the position-dependent upper and lower level populations, which enables us to accurately determine the spatial variation of the laser-ablated species in these states. Furthermore, the calculated profile is almost unchanged with temperatures employed for fittings. This means that the present method gives reliable values of the parameters for the spatial distributions, even if the temperature is not precisely known.

The role and effect of the isoelectronic center Sb on the structure and properties of GaN epilayers have been investigated. The gas phase Sb concentration was varied by changing the triethyl antimony/trimethyl gallium mole ratio over a wide range of concentrations while keeping other growth parameters constant. The Sb addition slightly improved the optical and structural properties of GaN epilayer at a low level of Sb incorporation, especially for the films grown under a high group V/III ratio conditions. The addition of Sb resulted in changes in GaN surface morphology, which was further explored by the lateral epitaxy overgrowth (LEO) technique through the changes in the growth rates and the facet formation. The presence of Sb in the gas phase greatly enhanced the lateral overgrowth rate and altered the formation of the dominant facets. Vertical facets to the LEO growth appeared with the addition of Sb under conditions that normally produced sloped sidewalls. While Sb altered the growth facet present during LEO, only a small amount of Sb was incorporated into the GaN, suggesting that Sb acts as a surfactant during the GaNmetal organic vapor phase epitaxygrowth.Sb addition produces surface conditions characteristic of a Ga-rich surface stoichiometry indicating both a possible change in the reactivity of and/or enhanced surface diffusion of Ga adatom species in the presence of Sb.

Electron irradiation induced phase decomposition in an alkaline earth multi-component oxide glass has been observed in a scanning transmission electron microscope. Separate regions that are rich and poor in alkaline earths form rapidly during the initial irradiation. In other words, alkaline earth multi-component oxide glasses are intolerant of high-energy (∼100 kV) electrons. This could result from the characteristics of a nonbridging O atom that bound to both Si (covalent) and alkaline earths (ionic). A modified Knotek–Feibelman model has been introduced to interpret the breakaway of cations from the glass network. Driven by electrostatic forces, the cations prefer to segregate, forming a cation rich region to reduce the amount of nonbridging O.

The surface evolution of highly oriented pyrolytic graphiteirradiated with ions of 1.0 keV at doses between and during annealing was investigated by scanning tunneling microscopy(STM) and atomic force microscopy(AFM) in the tapping mode. Hillocks were observed by both STM and AFM after ion irradiation, where the height of a hillock measured by STM was larger than that measured by AFM. The ion-irradiated surface was recovered in three stages during annealing: the first stage at 473–873 K, the second stage at 873–1473 K, and the third stage at 1473–1873 K. In the first stage, many of the ion-induced hillocks recovered rapidly and irregular domelike protrusions were formed due to both the recombination of the mobile interstitial clusters with the immobile vacancies and the aggregation of interstitial clusters. In the second stage, the hillocks recovered slightly and domelike protrusions aggregated to larger domelike protrusions. In the third stage, the hillocks recovered completely and domelike protrusions changed from irregular shapes to regular circles with monatomic step height of graphite due to the change from irregular carbon interstitial clusters to complete extraplane in graphite. Hexagonal hollows were also formed and became larger circular hollows above 1623 K with monatomic step height of graphite due to the vacancy clusters formed by the migration of vacancies and the following collapse of the neighboring layers in graphite.

We discuss results of surface photovoltage (U) measurements for μm thick layers of undoped hydrogenated microcrystalline silicon-Si:H). By applying excitation with low energetic photons (down to 1.1 eV), i.e., with small absorption coefficient α and a large penetration depth a photovoltage peak appears on a curve This peak is located at and its occurrence depends critically on the substrate material. The peak is present in a -Si:H film grown on crystalline silicon (c-Si), on the other hand it is missing in the -Si:H samples grown on c-Si or ZnO film. We present a mathematical model that enables us to link this peak to photocharge separation in the bottom space charge region at the interface -Si:H/substrate. Besides the magnitude of the ambipolar carrier diffusion length L, a parameter particularly critical for the occurrence of the peak turns out to be the ratio n of reverse saturation current densities of the two diodes representing surface and bottom space charge regions. The peak can be observed only when is below a certain threshold value In the simplified case when and when the thicknesses of the upper and lower depletion layers can be neglected, we have found or 1, depending on the orientation of the top and bottom barriers to each other. However, the magnitude of the peak increases exponentially with further lowering of Therefore, the surface photovoltage method is suitable not only for evaluating the minority carrier diffusion length L, but also for detecting the occurrence and properties of the bottom space charge region in thin film solar cells.

Gallium oxide thin filmsdeposited by electron cyclotron resonanceplasmamolecular beam epitaxy on GaAs(110) surfaces are reported. Room temperature photoluminescence spectra show an enhancement over as-is surfaces by greater than an order of magnitude for semi-insulating wafers. This enhancement is corroborated by low temperature photoluminescence spectra, showing a reduction in and carbon-related emissions. The bonding configuration at the interface to GaAs was investigated by x-ray photoelectron spectroscopy depth profiling and secondary ion mass spectroscopy: Arsenic oxide related compounds were below the sensitivity limits of the former technique, while carbon (both in the film and in the vicinity of the interface) was below the sensitivity limit of the latter technique. Photoluminescence enhancement is also attributed to hydrogen passivation of EL2 defects, which is found to be stable following deposition at temperatures of 400 °C on semi-insulating and p-type wafers.

Hydrogen implantedsilicon has been shown to cleave upon annealing, thus facilitating the transfer of thin silicon slices to other substrates, a process known as “ion-cut.” In our experiments 〈100〉 silicon wafers were implanted with 40 keV protons to a variety of ion doses ranging from to and subsequently annealed at 600 °C. The samples were studied before and after annealing by a combination of Rutherford backscatteringspectroscopy in channeling mode, elastic recoil detection analysis,atomic force microscopy, and electron microscopy. Mechanical stresses in the material, caused by proton irradiation, were determined by measuring changes in curvature of the silicon samples utilizing a laser scanning setup. For H doses of ion cutting in the form of “popping off” discrete blisters was obtained. Our analyses of the cleavage mechanisms had shown that the ion-cut location in silicon is largely controlled by the lattice damage that is generated by the H implantation process. At lower H doses, the location of the cut correlates well with the damage peak and can be explained by damage induced in-plane stress and the corresponding elastic out-of-plane strain. However, at higher implantation doses the ion-cut location shifts toward a deeper region, which contains lower damage and a sufficient concentration of H. This effect can be explained by a rapid decrease of the elastic out-of-plane strain coinciding with changing fracture mechanics at high H concentrations in heavily damaged silicon.

In the present study, reduction in the linear density of twinning dislocations resulting from the simultaneous application of high-density electric current pulses (40 A/mm2 for 400 μs) and constant magnetic field (with induction in 0.2 T) to bismuth crystals has been found. Current pulses and constant magnetic field were applied to the specimen after the deformation was introduced by a concentrated load and pileups of twinning dislocations were created. It has been clearly shown that the decrease in the linear density of twinning dislocations results in the elongation of the deformation twins. This effect occurs despite the increase of the number of twinning dislocations with an increase in the concentrated load. The experimental facts are in good accord with the modern concept of the electroplastic effect.

The applicability of the laser flash method for measuring the thermal diffusivity of highly porous cordierite materials is investigated. Due to the surface roughness of the samples, some indetermination in the sample thickness measurement is produced, which induces errors in the thermal diffusivity calculation. This problem was partially overcome by attaching two thin Cu layers to both surfaces of the samples. The thermal diffusivity and conductivity values of two porous cordierite materials (40 and 50 vol % of porosity) are reported using this procedure and results are discussed comparing with data for three-layer models.